The present application is based on Japanese Patent Application No. 2001-312162, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a wide viewing angle polarizer adapted for improvement in viewing angle characteristic of a liquid-crystal display device such as a vertical aligned (VA) liquid-crystal display device.
2. Description of the Related Art
To form a liquid-crystal display device exhibiting excellent display quality in all azimuths by compensation for birefringence of a liquid-crystal cell achieving display through a polarizer, the polarizer needs to be combined with a phase retarder in which main refractive indices nx, ny and nz in three directions, that is, two in-plane directions x and y in association an obliquely viewing direction and one normal direction z, are controlled. Particularly in a VA or OCB liquid-crystal display device, the polarizer needs to be combined with a phase retarder in which the main refractive indices in the three directions satisfy the relation nx greater than ny  greater than nz.
As the phase retarder with controlled nx, ny and nz used in combination with the polarizer, there is heretofore known a phase retarder made from uniaxially stretched films laminated so that in-plane slow axis directions are perpendicular to each other or a monolayer phase retarder formed from a high-molecular film laterally or biaxially stretched by a tenter. Each of these phase retarders is bonded to a polarizer having a transparent protective layer such as a triacetyl cellulose film through an adhesive layer to thereby form an object.
Use of the former phase retarder, however, brings about a problem that the volume of the phase retarder is large because of use of two retardation films. On the other hand, the range of retardation value obtained in the latter monolayer phase retarder is narrow. In the case where the latter monolayer phase retarder is used and retardation value in the direction of the thickness of the phase retarder is remarkably larger than that in the normal direction, two or more phase retarders need to be laminated in the same manner as the former phase retarder in order to obtain the required retardation value. There arises still the problem that the volume of the phase retarder is large.
An object of the invention is to provide a phase retarder-containing polarizer which is excellent in reduction in thickness and which can be used for forming a liquid-crystal display device such as a VA liquid-crystal display device improved in viewing angle characteristic and high in contrast.
According to the invention, there is provided a wide viewing angle polarizer having: a polarizing film; and a phase retarder adhesively laminated on at least one surface of the polarizing film through an adhesive layer, the phase retarder being made of a composite phase retarder constituted by a laminate in which a retardation layer B of a cholesteric liquid crystal-oriented solidified layer in a selective reflection wavelength range of not larger than 350 nm is supported by a retardation layer A of a thermoplastic resin exhibiting positive birefringence, the composite phase retarder being formed so that the laminate has Re of not smaller than 10 nm and Rthxe2x88x92Re of not smaller than 50 nm on the basis of light at a wavelength of 590 nm when Re and Rth are defined as Re=(nxxe2x88x92ny)X d and Rth=(nxxe2x88x92nz)X d respectively in which nx and ny are in-plane main refractive indices, nz is a thicknesswise refractive index, and d is a layer thickness. There is also provided a liquid-crystal display device having: a liquid-crystal cell; and a wide viewing angle polarizer defined above and disposed on at least one surface of the liquid-crystal cell.
According to the invention, the retardation layer B is excellent in reduction in thickness because it is made of a liquid-crystal coating film. Moreover, because the retardation layer B is supported by the retardation layer A, a high-quality composite phase retarder excellent in reduction in thickness can be obtained. Moreover, because the composite phase retarder is bonded to a polarizing film so as to serve as a transparent protective layer, a separate transparent protective layer to be bonded to the polarizing film can be omitted. Hence, greater reduction in thickness can be achieved. When the combination of the composite phase retarder and the polarizing film is used, the viewing angle of the liquid-crystal cell can be improved extremely.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.